how to refer to partial list, slice is too slow?

["Martin v. Lo"wis"]

人言落日是天涯，望极天涯不见家 schrieb:
> I'm a python newbie. It seems the slice operation will do copy.
> for example:
>>>> a = [1,2,3,4,5,6,7,8,9,0]
>>>> b = a[7:]
>>>> b
> [8, 9, 0]
>>>> a.remove(9)
>>>> a
> [1, 2, 3, 4, 5, 6, 7, 8, 0]
>>>> b
> [8, 9, 0]
> 
> if the list have large members, the slice operations will consume many
> times.
> for instance, I have a long string named it as S, the size is more
> than 100K
> I want to parser it one part-to-part. first, I process the first 100
> byte, and pass the remainder to the next parser function. I pass the
> S[100:] as an argument of the next parser function. but this operation
> will cause a large bytes copy. Is there any way to just make a
> reference to the remainder string not copy?

You can use itertools.islice:

py> a = [1,2,3,4,5,6,7,8,9,0]
py> b = itertools.islice(a, 7)
py> b
<itertools.islice object at 0xb7d9c34c>
py> b.next()
1
py> b.next()
2
py> b.next()
3
py> b.next()
4
py> b.next()
5
py> b.next()
6
py> b.next()
7
py> b.next()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
StopIteration

HTH,
Martin